1. To increase volume and depth of your voice, breathe in before you speak and let the words leave your mouth with the air so that you speak from your chest rather than your throat.
2. Don't hold anything in your hand, like water bottles or pens. There seems to be a tendency for people to fiddle excessively with stuff in their hands whilst they are giving oral presentations, it's distracting and it displays nervousness.
3. Don't speak too fast. Don't try to complete a speech made for twice the available time by racing against the clock. This is probably the most common mistake. Literally nothing will register and the audience will endure a frustrating ordeal. On the other hand don't speak so slow that the audience will lose all interest.
4. Stance is sometimes a problem. Some speakers stand still particularly behind a lectern. Others tend to wander all over the stage. A wandering speakers needs to consider whether his physical meanderings are distracting the audience's attention from what he is saying. The best thing to do is to be relaxed and stand up straight.
5. Keep eye contact with the audience. But be careful not to pick one person (usually it's the teacher) who is the sole recipient of your eye contact. This can be incredibly embarrassing to that person and annoying to everyone else. Your eye should wander over and encompass the whole audience so as to give each individual the impression that the speech is directed at him or her.
6. Dress appropriately. Tuck your shirt in, do your tie properly, don't look as if you are about to go to the beach.